Went for my first longer drive yesterday, about 40 miles. With the gage between 3/4 and full this 1008 took 7.5 gallons. Book says it's a 20 gallon tank. Is this normal for these gages? Also, do you fill it until it starts to back up in the filler neck? That's a big filler pipe. And what mileage should I expect?...At 50mph, even up to 52/53, it was quieter than I thought it would be. At 55, just 2 mph more, there is a really LOUD exhaust sound. Is this normal? The whole exhaust system looks good, no real rust etc.